We study allosteric modulation of neuronal nicotinic acetylcholine receptors (nAChRs). These ligand-gated ion channels are the seat of nicotine addiction and are implicated in a wide range of other neurological disorders. Allosteric modulation of nAChRs is growing in importance as it becomes better understood and as novel compounds with this pharmacological profile are identified. The binding sites for a class of model modulatory compounds, quite specific for one subtype of neuronal nAChR, are known, and some molecular determinants of transducing modulator binding information into channel activity have been identified. Building on this previous work, we now propose to further refine our understanding of the movement of one sub- structure involved in intra-molecular signal transduction and of the molecular determinants of modulator site specificity. In addition, questions about channel gating efficacy will be addressed in terms of the optimal number and arrangement of modulator sites relative to agonist sites and the role of hydrophobic residues in the extracellular domain core. These studies will employ pharmacological characterization of expressed receptors with point mutations or concatenated subunits by macroscopic voltage-clamp recordings, as well as chemical modification analyses. The project also includes a targeted structure-activity relationship study with new modulator analogues. In some cases, to support these primary aims, we will explore the modulation mechanisms further by single-channel recordings. Our work is innovative because we are challenging the paradigm of activation of nAChRs by occupying two agonist binding sites. We are studying a recently identified nAChR ligand binding site, and the work we propose stands to substantially strengthen the foundation for rational design of nAChR allosteric modulators, a drug class with possible clinical applications.